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40mm Plossl in Mark Vs

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#1 Eddgie

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Posted 11 January 2013 - 10:39 AM

Just a quick report with some background.

While I like a wide appearent field, and the 24mm Hyperions do provide that, it comes at the expense of rather high magnification. I estimate that the 24mm Hyperions give about 165x in the C14.

The problem with this is two-fold. First, I am already loosing some brightness because of the binoviewers, and second, even when seeing is fairly good, stars will start to flare at this power, so the brigther stars in brighter clusters will look a bit soft, and for nebula, the loss of brightness means they don't stand out quite so well.

The simplest way to address this is to lower the magnification, and indeed, the 41mm Panoptic was one of my most used eyepeices in the C14 prior to the Binoviewers.

I can't get back the true field that the binoviewers take from me, but I can get back some of the brightness, and this motivated me to buy a pair of Televue 40mm Plossls. An expensive risk, but at the same time, the resale is good enough that I felt I could recover most of the money spent.

Took them out for a flight last night.

Of course my major concern was the narrow apparent field. There have been accounts on this forum that using narrow apparent field eyepeices in binoviewers does not seem a restrictive as when using them in mono-vision mode and I am going to now say that.

While it was easily evident that the AFOV was narrower, it did not feel quite as restrictive as in Mono-mode. Narrow, but then again, less confining that I would have expected. I spent quite a bit of time going after larger brighter clusters and was not at all bothered by the narrow apparent field.

In some respects, it actually worked better because I could take in more of the field simply by looking straight into the eyepeice rather than have to turn my eyes to one side or the other, which can sometimes cause blackouts in wide field eyepeices.

As for brightness and sharpness, once again, I was very pleased. The lower magnification and larger exit pupil restored much of the brigtness to the view. While the sky was brighter, stars just seemed to be more pleasing because they were smaller, sharper points and the lower magnification make it difficult to see as much flaring that seeeing causes. Clusters looked great! I viewed M35, M36, M37, M46, and NGC 869 (half of double cluster) and compared the 24/68s to the 40/43s and got the same feeling in every case... The clusters all looked brigher and sharper in the 40/43s.

I then went to Orion. This was a big test for how a Nebula would benefit from the improved brightness. Now while the true field is the same, the scale is obviously much smaller, so I was concerned about how this would look in the eyepeice. Yes, it was smaller, but not so small as to be hard to see major structure. Also, no surprise because it was this way in the 41mm Pan as well, the Trapezium was easy as was the E and F components.

Overall, Orion did indeed look brighter and major details did seem to stand out better from the background and this is of course consistent with the effects of a bigger exit pupil.

The downside was that the eye relief is overly long, and I had a bit of trouble staying aligned to the exit pupil. It seemed harder to hold still vs the 41mm Pan.

And speaking of that, I did put in the 41mm Pan. Ok, was going to try to go binoviewing exclusivly for a while, but could not resist for comparison purposes. I won't be selling the 41mm Pan anytime soon, as it easily gave a more expansive and pleasing view.

But for things that will fit into the field (M27, M1, and other medium size Nebula) it is nice to know that I don't have to drop the binoviewes and diagonal to replace them with the 41mm Pan and 2" diagonal.

And as an experiment, I am happy I did it. I think that for many clusters, I might enjoy the more pinpoint appearance offered by the 40s.

This is in a C14 though. Still, I think larger SCT owners may find an inexpensive pair of 40mm Plossls to be a nice compliment when they need the brightest view possible. The apparent field limitation did not impact me nearly to the extent I had expected. In fact, it did not seem so different from using 50 degree AFOV eyepeices in mono-mode.

The Televues were nice, but I just don't know if you would have to spend that much money to duplicate the major benefit offered.

Of course only people using large prism units will get the full benefit of this because smaller units will likely vignette with 40s, but for someone using something like 19mm Pans in their refractor as their low power eyepiece, you could get a partial benefit by keeping some 25mm Plossls for times when you just need a bit brighter view.

Such a complex environment... Just thought I would share and hope it is useful to others.

#2 Mr. Bill

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Posted 15 January 2013 - 04:27 PM

....The downside was that the eye relief is overly long, and I had a bit of trouble staying aligned to the exit pupil. It seemed harder to hold still vs the 41mm Pan.


I have same problem with my TV 32mm Plossls in my Denk IIs....seems hard to merge fields as well as centering exit pupil.



Of course only people using large prism units will get the full benefit of this because smaller units will likely vignette with 40s, but for someone using something like 19mm Pans in their refractor as their low power eyepiece, you could get a partial benefit by keeping some 25mm Plossls for times when you just need a bit brighter view.


Or just use 24mm Pans with their 68 degree fovs.

:cool:

#3 Eddgie

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Posted 15 January 2013 - 08:13 PM

You don't get nearly the same exit pupil with the 24mms. Nebula look much brighther in the 40s.

#4 Sergio E

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Posted 22 January 2013 - 03:03 PM

I've bought the two TV pl 40mm second hand.
:confused:
One with blue glass.
The other with green glass.

On the Jupiter just for try which one was better.

The blue one were more performant, maby becouse the blue helped, like a filter :)

Normally I d'nt find any differences on the bino Mark V.

Same time ago I've bought two Tv pl 32mm for my Miyuchi Saturn III, in my opinion the 40mm are far more performant.

On the Mark V in alternative at the tv pl 32mm I prefer the Taka Le 30mm.
Sergio

PS I've recovered my old username Sergio E so SergioEn disappear ;)

#5 DRodrigues

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Posted 23 January 2013 - 02:29 PM

The downside was that the eye relief is overly long, and I had a bit of trouble staying aligned to the exit pupil.

You have to use 40mm eyepieces with adjustable eye-guard like the GSO SuperViews or the Vixen NPL or NLV - for the best image quality and TFOV use the NLV40. I have these and used these in my daylight combo http://www.pt-ducks....#CR-binoviewing resulting in the best image quality solution I tried. Why I don't use it regularly? Because I need higher magnifications/resolution. However comparing the NLV40 with the TS32SuperView, the resulting AFOV seemed similar since the NLV40 has larger TFOV and better image quality...

#6 faackanders2

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Posted 23 January 2013 - 11:57 PM

You don't get nearly the same exit pupil with the 24mms. Nebula look much brighther in the 40s.


24mm panoptics (widest TFOV with 1.25") should provide majesty factor of darker skies and higher contrast, compared to Possils, and not sacrifice TFOV.






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